Controlling vehicles which do not contain human operators presents many challenging obstacles. The problem involves, in one case, having a convoy of vehicles following a lead vehicle. The lead vehicle contains a human operator and sends position data to the follower vehicles as the lead vehicles travels down a road. The follower vehicles do not require human operators; they receive the position data from the lead vehicle and must be able to use that data in maintaining a correct path along the road.
Another example of the problem involves a vehicle with a human operator being driven down a road as sensors on board the vehicle gather position information. The position data is stored in a data storage device, such as a floppy disk. Subsequent to the lead vehicle's trip, the position data may be loaded into other vehicles which then use the position data to travel the same path as the lead vehicle without requiring human operators.
A number of different systems have been developed in an attempt to control vehicles without requiring human operators. These systems include the following.
A radio frequency navigation grid utilized three stationary transmitters to control a vehicle's motion within an area defined by the locations of the transmitters. The transmitters included a master transmitter and two slaves. A receiver on board a lead moving vehicle sensed the phase relationships of the arrival of the signals transmitted from the three stations. The lead vehicle recorded these phase relationships while traveling down a particular path within the defined area. During subsequent retrace drives by vehicles without operators, the real-time received phase relationships were compared to the stored phase relationships from the lead vehicle. The retrace vehicle was then commanded to move in the direction that minimized the differences between the real time signal and the stored phase relationships. This system had an error such that a retrace vehicle could follow the original path to within a few feet. An implementation of the system, the Kaman Sciences System, was limited to approximately a 5.times.5 kilometer area as outlined by the three transmitters.
A ring laser gyro system, developed by Honeywell, Inc. Systems and Research Center in cooperation with the Advanced Systems Center of Honeywell's Defense Systems Division, determined waypoints along a driven path using a ring-laser-gyro-based inertial navigator. During a training drive by a vehicle, the system recorded the waypoints. After the completion of the learning path drive, the vehicle retraced the learned path by comparing its real-time, inertially-derived location with the previously recorded waypoints. The system caused the vehicle to move in a direction so as to minimize the difference obtained by the comparison. This system had a typical error of approximately one foot over a path of approximately 1000 feet and suffered from an unbounded error growth.
A pre-positioned target plaques system used coded plaques similar to the universal bar codes used by supermarkets. The coded plaques were placed at various locations along a path or around a work area in which an unmanned vehicle was to operate. A scanning laser in the vehicle scanned over the coded plaques and identified each by its unique code. Based on the angle of the laser beam and the range to the target plaque, the system determined the location of the vehicle from the laser readings. A limitation of this system was the requirement of markers along the desired path.
An embedded wire system used a wire or similar path marker embedded in the roadway to guide a vehicle. Sensors mounted in the front of the vehicle sensed the vehicle's position relative to the embedded marker, and the system guided the vehicle based upon this information. This system had been discussed for many years as part of an automated highway system. A major factor with this system was the high cost of modifying highways to include the embedded wire.
All of the systems described above have certain limitations which have created a need for a new solution to the problem. Systems which required external markers, such as the embedded wire or coded plaques, restricted the vehicle's motion to a specific path or area. Likewise, the system that used a navigation grid had a limited area in which to operate and required external transmission stations. The ring laser gyro system was less limited in terms of the area in which it may have been used; however, the system had significant errors which tended to grow larger over a longer path, which inherently restricted the range of the system.